Optical information medium and production method therefor

ABSTRACT

The present invention provides an optical information medium that is less susceptible to warp in the disk surface while offering significantly high scratch resistance and abrasion resistance, and a method for producing the optical information medium. An optical information medium ( 1 ) comprising a supporting substrate ( 2 ) and a film element, the film element disposed on the supporting substrate ( 2 ) and composed of one or more layers including at least a recording layer ( 5 ) or a reflective layer ( 3 ), wherein at least one of the supporting substrate-side surface and the film element-side surface is formed of a hard coat layer ( 9 ) of a cured product of a composition comprising (A) inorganic fine particles with an average particle size of 100 nm or less, (B) a reactive silicone, and (C) an active energy ray-curable compound.

TECHNICAL FIELD

The present invention relates to optical information media, such asread-only optical disks, optical recording disks, and magneto-opticalrecording disks, as well as to production methods for such opticalinformation media. More specifically, the present invention relates tooptical information media that are less susceptible to warp in the disksurface and at the same time offer significantly high scratch resistanceand abrasion resistance. The invention also relates to productionmethods for such optical information media.

BACKGROUND ART

Polycarbonate resin materials and methyl methacrylate resin materialsare currently widely used in various optical information media asoptical materials of the light-transmitting layers and the like becauseof their moldability, transparency, and prices. One drawback of theseresin materials is their lack of sufficient scratch/abrasion resistanceand sufficient anti-staining property against organic stains. Anotherdrawback is that these resin materials are easily charged because oftheir high insulation, so that the surfaces of the optical informationmedia may pick up substantial amounts of dust particles during storageor use of the media, causing errors in recording/reproducing of opticalinformation.

To improve the scratch resistance of the surface of media, atransparent, scratch-resistant hard coat is generally formed on thesurface of the light-transmitting layer of the media. This is done byapplying an active energy ray-polymerizable/curable compound onto thesurface of the light-transmitting layer and subsequently irradiatingactive energy rays, such as ultraviolet rays, onto the surface to curethe compound. The active energy ray-curable compound typically includes,within its molecule, two or more polymerizable functional groups, suchas (meth)acryloyl groups, that take part in polymerization. Although thehard coat obtained in this manner has higher abrasion resistance ascompared to the surface of the resin films made of a polycarbonate,methyl(meth)acrylate and the like, the highest achievable abrasionresistance is still limited and the hard coat does not necessarilyprovide sufficient scratch resistance required during the use of themedia. Use of harder resins to improve the scratch resistance generallyresults in an increase in the shrinkage of the hard coat upon curing, sothat the resulting medium tends to suffer significant warp in the disksurface. Since the sole purpose of such hard coats is to improve thescratch resistance, the coatings generally fail to achieve sufficientanti-staining property against various contaminants, including dustparticles, oil mist in the atmosphere, and fingerprints.

A hard coat having anti-staining property against organic stains isdescribed in Japanese Patent Laid-Open Publication No. Hei10-110118(1998). Such a hard coat can be fabricated by admixing anon-crosslinking fluorine-based surfactant to a hard coat agent.However, the non-crosslinking fluorine-based surfactant in the hard coatagent is gradually lost as the media are repeatedly cleaned by, forexample, wiping over the course of their use.

It is suggested in Japanese Patent Laid-Open Publication No. Hei11-213444(1999) to apply a fluorine-based polymer onto the surface ofsubstrates of optical disks made of conventional materials such aspolycarbonate. However, the fluorine polymer is physically adsorbed tothe surface of the substrates only through the effect of van der Waalsforce, so that the adhesion of the fluorine-based polymer to thesubstrates surface is considerably weak. Thus, the surface treatmentwith the fluorine-based polymer coating poses a significant problem interms of durability.

It is suggested in European Patent Publication No. EP1146510A2 to addmetal chalcogenide fine particles such as silica fine particles to ahard coat to improve the scratch resistance of the hard coat. A film ofa water repellant group or an oil repellent group-containing silanecoupling agent is then applied over the hard coat to improve theanti-staining property of the surface.

DISCLOSURE OF THE INVENTION Objects of the Invention

By making the coefficient of friction of the medium surface low, animpact caused when a hard projection contacts the surface can be slippedaway; therefore, the generation of scratches can be suppressed. For thisreason, it is desired to decrease the coefficient of friction of thesurface of the hard coat to improve the scratch resistance of thesurface. In recent years, attempts have been made to increase theinformation recording density of digital data-recording media byreducing the spot size of focused recording/reproducing laser beams.This is achieved by increasing the numerical aperture (NA) of anobjective lens to focus the recording/reproducing laser beam to a valueof 0.7 or higher, for instance, to approximately 0.85, and at the sametime reducing the wavelength λ of the recording/reproducing laser beamto approximately 400 nm. However, increasing NA generally leads to adecreased distance between the objective lens and the surface of theoptical information medium (i.e., working distance), which significantlyincreases the likelihood that the surface of the optical informationmedium will come into contact with the objective lens, or the support ofthe lens, during the rotation of the optical information medium (forexample, for NA of approximately 0.85, working distance is approximately100 μm, a significant decrease from conventional optical systems). Forthis reason, it is desired to reduce the coefficient of friction of thehard coat surface while increasing the scratch resistance of thesurface.

Addressing the above-identified problems of prior art, it is anobjective of the present invention to provide an optical informationmedium that is less susceptible to warp in the disk surface and at thesame time offers significantly high scratch resistance and abrasionresistance. It is another objective of the present invention to providea production method for such an optical information medium that is lesssusceptible to warp in the disk surface and at the same time offerssignificantly high scratch resistance and abrasion resistance.

SUMMARY OF THE INVENTION

The present inventors made eager investigation. As a result, the presentinventors have found that an optical information medium that is lesssusceptible to warp in the disk surface while offering significantlyhigh scratch resistance and abrasion resistance can be obtained byforming at least one surface of the medium, preferably, the laser beamincident surface, as a hard coat layer that is formed of a cured productof a particular composition that comprises fine particles with anaverage particle size of 100 nm or less; a reactive silicone; and anactive energy ray-curable compound.

Thus, the present invention comprises the followings:

(1) An optical information medium comprising a supporting substrate anda film element, the film element disposed on the supporting substrateand composed of one or more layers including at least a recording layeror a reflective layer, wherein at least one of the supportingsubstrate-side surface and the film element-side surface is formed of ahard coat layer of a cured product of a composition comprising:

(A) inorganic fine particles with an average particle size of 100 nm orless;

(B) a reactive silicone; and

(C) an active energy ray-curable compound.

(2) The optical information medium according to (1) above, wherein theinorganic fine particles (A) are fine particles of a metal (or asemi-metal) oxide, or fine particles of a metal (or a semi-metal)sulfide.

(3) The optical information medium according to (1) or (2) above,wherein the inorganic fine particles (A) are fine particles of silica.

(4) The optical information medium according to (3) above, wherein thefine particles of silica are modified on the surface with a hydrolyzablesilane compound including an active energy ray-reactive group.

(5) The optical information medium according to any of (1) to (4) above,wherein the reactive silicone (B) comprises at least one reactive groupselected from the group consisting of (meth)acryloyl group, vinyl group,and mercapto group.

(6) The optical information medium according to any of (1) to (5) above,wherein the reactive silicone (B) comprises two or more (meth)acryloylgroups within its molecule.

(7) The optical information medium according to any of (1) to (6) above,wherein the composition comprises 5 wt % or more and 80 wt % or less ofthe inorganic fine particles (A), 0.01 wt % or more and 1 wt % or lessof the reactive silicone (B), and 19 wt % or more and 94.99 wt % or lessof the active energy ray-curable compound (C) with respect to the totalamount of the components (A), (B), and (C).

(8) The optical information medium according to any of (1) to (7) above,wherein the composition further comprises a photopolymerizationinitiator.

(9) The optical information medium according to any of (1) to (8) above,wherein information is optically recorded or reproduced by the lightincident upon the supporting substrate-side or the film element-side ofthe information medium.

(10) The optical information medium according to any of (1) to (9)above, wherein either one of the supporting substrate-side surface orthe film element-side surface upon which the light is incident is formedof the hard coat layer.

(11) A method for producing an optical information medium, comprisingthe steps of:

forming, on a supporting substrate, a film element composed of one ormore layers including at least a recording layer or a reflective layer;

applying a composition onto at least one of the surface of the filmelement and the surface of the supporting substrate opposite to the filmelement-formed side, the composition comprising (A) inorganic fineparticles with an average particle size of 100 nm or less, (B) areactive silicone, and (C) an active energy ray-curable compound; and

irradiating active energy rays onto the applied composition to cure thecomposition and to thus form a hard coat layer.

(12) The method for producing an optical information medium according to(11) above, wherein the composition further comprises a non-reactiveorganic solvent, and following the application of the composition andprior to the irradiation of the active energy rays to cure thecomposition and to thus form a hard coat layer, the non-reactive organicsolvent is removed by heat-drying.

(13) An optical information medium, obtainable by

forming, on a supporting substrate, a film element composed of one ormore layers including at least a recording layer or a reflective layer;

applying a composition onto at least one of the surface of the filmelement and the surface of the supporting substrate opposite to the filmelement-formed side, the composition comprising (A) inorganic fineparticles with an average particle size of 100 nm or less, (B) areactive silicone, and (C) an active energy ray-curable compound; and

irradiating active energy rays onto the applied composition to cure thecomposition and to thus form a hard coat layer.

As used herein, the term “optical information medium” is intended toencompass read-only optical disks, optical recording disks,magneto-optical recording disks, and other media.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross sectional view of one example of an opticaldisk of the present invention.

FIG. 2 is a diagram illustrating a manner by which the coefficient offriction of the optical disk is measured.

FIG. 3 is a graph showing the results of the measurement of thecoefficient of friction of the optical disk (cumulative number ofrotation versus coefficient of friction).

MODES FOR CARRYING OUT THE INVENTION

An optical recording medium (for brevity to be referred to hereinafteras “optical disk”) and a method for producing the same of the presentinvention will be described with reference to FIG. 1. Although thedescription will be given of a phase change type optical disk as anexample, the present invention is not limited to this, but is widelyapplicable to various optical disks with any type of recording layers,including read-only optical disks, and write-once optical disks and thelike.

FIG. 1 is a schematic cross sectional view of one example of an opticaldisk of the present invention. In FIG. 1, an optical disk (1) has asupporting substrate (2) having information pits, pregrooves, and otherfine scale concavities-convexities formed on one surface thereof. Onthis surface, the optical disk (1) has a reflective layer (3), a seconddielectric layer (4), a recording layer (5), and a first dielectriclayer (6) formed in this order, and further has a resin layer (7) on thefirst dielectric layer (6), a light transmitting layer (8) on the resinlayer (7), and a hard coat layer (9) on the light transmitting layer(8). In this example, a film element necessary for recording and/orreproducing is formed of the reflective layer (3), the second dielectriclayer (4), the recording layer (5), the first dielectric layer (6), theresin layer (7), and the light transmitting layer (8). When using theoptical disk (1), a laser beam for recording and/or reproducing isincident through the hard coat layer (9) and the light transmittinglayer (8), namely the film element side.

The supporting substrate (2) has a thickness of 0.3 to 1.6 mm,preferably of 0.5 to 1.3 mm, and includes information pits, pregrooves,and other fine scale concavities-convexities formed on the surface onwhich the recording layer (5) is formed.

The supporting substrate (2) is not required to be optically transparentwhen the optical disk (1) is used in such a manner that a laser beam isincident through the film element side as described above, while isrequired to be optically transparent when the optical disk (1) is usedin such a manner that a laser beam is incident through the side of thesupporting substrate (2). As transparent materials, various plasticmaterials including polycarbonate resins, acrylic resins such aspolymethyl methacrylate (PMMA), and polyolefine resins and the like maybe used. Such flexible materials are particularly useful in the presentinvention since the present invention can control their warping. Itshould be noted, however, that glass, ceramics or metals and the likemay be also used for the supporting substrate. If a plastic material isemployed, the pattern of the concavity-convexity in the surface will beoften produced by injection molding, whereas the pattern will be formedby a photopolymer process (2P process) in the case of any material otherthan plastics.

The reflective layer (3) is usually deposited by a sputtering process onthe supporting substrate (2). As a material for the reflective layer, ametallic element, semi-metallic element, semiconductor element or acompound thereof may be used singly or compositely. More specifically,the material may be selected from known materials for the reflectivelayers such as Au, Ag, Cu, Al, and Pd. The reflective layer ispreferably formed as a thin film with a thickness of 20 to 200 nm.

The second dielectric layer (4), the recording layer (5), and the firstdielectric layer (6) are deposited in this order by sputtering processon the reflective layer (3), or on the supporting substrate (2) in thecase that no reflective layer is provided.

The recording layer (5) is formed of a material changing reversibly byirradiation of laser beam between the crystalline state and theamorphous state, and exhibiting different optical properties betweenthese states. Examples of such material include Ge—Sb—Te, In—Sb—Te,Sn—Se—Te, Ge—Te—Sn, In—Se—Tl, and In—Sb—Te. Further, to any suchmaterial, a trace of at least one metal selected from Co, Pt, Pd, Au,Ag, Ir, Nb, Ta, V, W, Ti, Cr, Zr, Bi, In and the like may be added. Atrace of reductive gas such as nitrogen also may be added. There is nolimitation to the thickness of the recording layer (5), which is forexample in a range of about 3 to 50 nm.

The second dielectric layers (4) and the first dielectric layer (6) areformed on the top and under surfaces of the recording layer (5),respectively, so as to sandwich the same. The second dielectric layers(4) and the first dielectric layer (6) have not only a function ofprotecting the recording layer (5) mechanically and chemically but alsoa function as an interference layer for adjusting the opticalproperties. The second dielectric layers (4) and the first dielectriclayer (6) may each consist of either a single layer or a plurality oflayers.

The second dielectric layers (4) and the first dielectric layer (6) ispreferably formed of an oxide, a nitride, a sulfide, or a fluoride or acomposite thereof, containing at least one metal selected from Si, Zn,Al, Ta, Ti, Co, Zr, Pb, Ag, Zn, Sn, Ca, Ce, V, Cu, Fe, and Mg. Further,the second dielectric layers (4) and the first dielectric layer (6)preferably have an extinction coefficient k of 0.1 or less.

There is no limitation to the thickness of the second dielectric layer(4), which is preferably for example in a range of about 20 to 150 nm.There is no limitation to the thickness of the first dielectric layer(6), either, which is preferably for example in a range of about 20 to200 nm. Setting the thicknesses of the second dielectric layers (4) andthe first dielectric layer (6) in these ranges makes it possible toadjust reflection.

The resin layer (7) having light transmission properties is formed onthe first dielectric layer (6) by using active energy ray-curablematerial.

The active energy ray-curable material should be optically transparent,exhibit low optical absorption or reflection in the laser wavelengthrange to be used, and have low birefringence, and is selected fromultraviolet ray-curable materials, electron ray-curable materials andthe like on these conditions.

Specifically, the active energy ray-curable material is constitutedpreferably of the ultraviolet ray-(electron ray-) curable compound orits composition for polymerization. Examples include monomers,oligomers, polymers and the like in which groups to be crosslinked orpolymerized by irradiation with ultraviolet rays, such as acrylic typedouble bonds such as in ester compounds of acrylate and methacrylate,epoxy acrylates and urethane acrylates, allyl type double bonds such asin diallyl phthalate, and unsaturated double bonds such as in maleicacid derivatives and the like have been contained or introduced into amolecule. These are preferably polyfunctional, particularlytrifunctional or more, and may be used alone or in combination thereof.While monofunctional ones may be used for necessary.

The ultraviolet ray-curable monomer is preferably a compound with amolecular weight of less than 2000, and the oligomer is preferably acompound with a molecular weight of 2000 to 10000. These includestyrene, ethyl acrylate, ethylene glycol diacrylate, ethylene glycoldimethacrylate, diethylene glycol diacrylate, diethylene glycolmethacrylate, 1,6-hexane glycol diacrylate, 1,6-hexane glycoldimethacrylate etc., and particularly preferable examples includepentaerythritol tetra(meth)acrylate, pentaerythritol (meth)acrylate,trimethylolpropane tri(meth)acrylate, trimethylolpropanedi(meth)acrylate, (meth)acrylate of phenol ethylene oxide adduct, etc.Besides, the ultraviolet ray-curable oligomer includes oligoesteracrylate, acrylic modified urethane elastomer etc.

The ultraviolet ray-(electron ray-) curable material may contain knownphotopolymerization initiators. The photopolymerization initiator is notparticularly necessary when electron rays are used as the active energyrays. However, when ultraviolet rays are used, the initiator isnecessary. The photopolymerization initiator may be properly selectedfrom the usual photopolymerization initiators such as acetophenone,benzoin, benzophenone, thioxanthone. Examples of a radical photoinitiator, among the photopolymerization initiators, include DAROCURE1173, IRGACURE 651, IRGACURE 184, and IRGACURE 907 (all of which areproducts manufactured by Ciba Specialty Chemicals Inc.). The content bypercentage of the photopolymerization initiator is, for example, fromabout 0.5 to 5 wt % with respect to the ultraviolet ray-(electron ray-)curable component.

As the ultraviolet ray-curable material, a composition containing epoxycompound and a photo-cation polymerization catalyst is also preferablyused. The epoxy compound is preferably alicyclic epoxy compound,particularly the compound having 2 or more epoxy groups in the molecule.The alicyclic epoxy compound is preferably one or more of the followingcompounds: 3,4-epoxycyclohexyl methyl-3,4-epoxycyclohexane carboxylate,bis-(3,4-epoxycyclohexylmethyl) adipate, bis-(3,4-epoxycyclohexyl)adipate, 2-(3,4-epoxycyclohexyl-5,5-spiro-3,4-epoxy)cyclohexane-metha-dioxane, bis(2,3-epoxycyclopentyl) ether and vinylcyclohexene dioxide etc. Although the epoxy equivalent of alicyclicepoxy compound is not particularly limited, it is preferably 60 to 300,more preferably 100 to 200 for attaining excellent curable properties.

The photo-cation polymerization catalyst used may be any of known onesand is not particularly limited. For example, it is possible to use oneor more of the followings: metal fluoroborates and boron trifluoridecomplexes, bis(perfluoroalkyl sulfonyl) methane metal salts, aryldiazonium compounds, aromatic onium salts of the group 6A elements,aromatic onium salts of the group 5A elements, dicarbonyl chelate of thegroups 3A to 5A elements, thiopyrylium salts, the group 6A elementshaving MF6 anions (M is P, As or Sb), triaryl sulfonium complex salts,aromatic iodonium complex salts, aromatic sulfonium complex salts etc.,and it is particularly preferable to use one or more of the followings:polyaryl sulfonium complex salts, aromatic sulfonium salts or iodoniumsalts of halogen-containing complexions, and aromatic onium salts of thegroup 3A elements, the group 5A elements and the group 6A elements. Thecontent by percentage of the photo-cation polymerization catalyst is,for example, from about 0.5 to 5 wt % of the ultraviolet ray-curablecomponent.

The active energy ray-curable material used for the resin layerpreferably has a viscosity of 3 to 500 cp (at 25° C.).

The resin layer (7) can be formed by applying the active energyray-curable material onto the first dielectric layer (6) using the spincoating technique. The thickness of the resin layer (7) after curing maybe adjusted to approximately 1 to 50 μm.

Subsequently, a light-transmitting sheet to serve as thelight-transmitting layer (8) is placed on the still uncured resin layer(7) and the active energy rays, such as ultraviolet rays, are thenirradiated to cure the resin layer (7). As a result, thelight-transmitting sheet is adhered to serve as the light-transmittinglayer (8). The light-transmitting sheet may, for example, be apolycarbonate sheet with a desired thickness ranging from 50 to 300 μm.More specifically, the light-transmitting layer (8) is formed by placingthe polycarbonate sheet having a desired thickness on the still uncuredresin layer (7) in vacuum (0.1 atom or less), allowing the pressure toreturn to atmospheric pressure, and then irradiating ultraviolet rays tocure the resin layer (7).

Alternatively, the resin layer (7) may be formed to a sufficiently largethickness to serve also as the light-transmitting layer so that thepolycarbonate sheet can be dispensed with. In such cases, the resinlayer (7) may have a thickness of approximately 50 to 300 μm aftercuring. While the same active energy ray-curable materials as thosedescribed above may be used, the materials preferably have a viscosityof 1,000 to 10,000 cp (at 25° C.).

A composition for the hard coat layer is then applied onto thelight-transmitting layer (8) and active energy rays, such as ultravioletrays, electron rays, or visible rays, are then irradiated to cure thecomposition and to thereby form the hard coat layer (9). The compositioncontains (A) inorganic fine particles with an average particle size of100 nm or less, (B) a reactive silicone, and (C) an active energyray-curable compound other than those described in (B) above. Thecomponents of the composition for the hard coat layer are describedbelow.

The active energy ray-curable compound (C) for use in the compositionfor the hard coat layer may have any structure, provided that itcontains at least one active group selected from (meth)acryloyl group,vinyl group, and mercapto group. To ensure sufficient hardness of thehard coat, the active energy ray-curable compound preferably includes apolyfunctional monomer or a polyfunctional oligomer that contains, inone molecule, two or more, preferably three or more polymerizablegroups. If used in excess, the polyfunctional monomer or thepolyfunctional oligomer causes an increase in the contraction of thehard coat upon curing and, thus, a substantial warp in the disk, thoughthe hard coat will become sufficiently hard. It should be givenattention.

Among such active energy ray polymerizable compounds (C) examples of thecompound having (meth)acryloyl group include 1,6-hexanedioldi(meth)acrylate, triethylene glycol di(meth)acrylate, ethylene oxidemodified bisphenol A di(meth)acrylate, trimethylolpropanetri(meth)acrylate, pentaerythritol tetra(meth)acrylate,ditrimethylolpropane tetra(meth)acrylate, dipentaerythritolhexa(meth)acrylate, pentaerythritol tri(meth)acrylate,3-(meth)acryloyloxyglycerin mono(meth)acrylate, urethane acrylate, epoxyacrylate, and ester acrylate. However, the compound having(meth)acryloyl group is not limited to these examples.

Examples of the compound having vinyl group include ethylene glycoldivinyl ether, pentaerythritol divinyl ether, 1,6-hexanediol divinylether, trimethylolpropane divinyl ether, ethylene oxide modifiedhydroquinone divinyl ether, ethylene oxide modified bisphenol A divinylether, pentaerythritol trivinyl ether, dipentaerythritol hexavinylether, and ditrimethylolpropane polyvinyl ether. However, the compoundhaving vinyl group is not limited to these examples.

Examples of the compound having mercapto group include ethylene glycolbis(thioglycolate), ethylene glycol bis (3-mercaptopropionate),trimethylolpropane tris(thioglycolate), trimethylolpropanetris(3-mercaptopropionate), pentaerythritol tetrakis(mercaptoacetate),pentaerythritol tetrakis(thioglycolate), and pentaerythritoltetrakis(3-mercaptopropionate). However, the compound having mercaptogroup is not limited to these examples.

The active energy ray-curable compounds (C) contained in the compositionfor the hard coat layer may be used alone or in combination of two ormore thereof.

The inorganic fine particles (A) for use in the composition for the hardcoat layer have an average particle size of 100 nm or less, preferably20 nm or less, to ensure the transparency of the hard coat layer.Preferably, the average particle size of the inorganic fine particles(A) is 5 nm or larger to meet the requirements for making a colloidalsolution.

The inorganic fine particles (A) may, for example, be fine particles ofmetal (or semi-metal) oxides, or fine particles of metal (or asemi-metal) sulfides. Examples of the metals or semi-metals for theinorganic fine particles include Si, Ti, Al, Zn, Zr, In, Sn, and Sb.Aside from the oxides and sulfides, the inorganic fine particles (A) mayinclude selenides, tellurides, nitrides, and carbides. Examples of theinorganic fine particles include fine particles of silica, alumina,zirconia, and titania. Of these, silica fine particles are preferred.When added to the hard coat agent composition, such inorganic fineparticles enhance the abrasion resistance of the hard coat layer.

The silica fine particles are preferably surface modified with ahydrolyzable silane compound containing active energy ray-reactivegroups. Such reactive silica fine particles undergo a crosslinkingreaction when exposed to active energy rays during curing of the hardcoat and are fixed in the polymer matrix. One example of such reactivesilica fine particles is the one described in Japanese Patent Laid-OpenPublication No. Hei 9-100111 (1997), which is suitable for use in thepresent invention.

The reactive silicone (B) contained in the composition for the hard coatlayer may be of any type, provided that it imparts water repellencyand/or lubricity to the hard coat layer and it contains functionalgroups that cause polymerization to occur when exposed to active energyrays. For instance, the reactive silicone (B) may be a silicone compoundcontaining at least one active energy ray-polymerizable functional groupselected from (meth)acryloyl group, vinyl group, and mercapto group.

The silicone compounds may include compounds containing a moiety with asilicone-based substituent and at least one type of reactive groupselected from (meth)acryloyl group, vinyl group, and mercapto group.Specific examples include, but are not limited to, compounds asrepresented by the following formulae (1) to (3):R—[Si(CH₃)₂O]_(n)—R  (1)R—[Si(CH₃)₂O]_(n)—Si(CH₃)₃  (2)and(CH₃)₃SiO—[Si(CH₃)₂O]_(n)—[Si(CH₃)(R)O]_(m)—Si(CH₃)₃  (3)

wherein R is a substituent containing at least one type of reactivegroup selected from (meth)acryloyl group, vinyl group, and mercaptogroup; and n and m each represent the degree of polymerization.

These reactive silicones (B) may be used either individually or incombination of two or more.

When added to the composition for the hard coat layer, the reactivesilicone (B) imparts lubricity to the surface of the hard coat layer(9), thereby making the surface of the hard coat layer (9) lesssusceptible to scratches. Containing the active energy ray-polymerizablefunctional groups, the reactive silicone undergoes a crosslinkingreaction when exposed to the active energy rays during curing of thehard coat and is fixed in the polymer matrix. To ensure that thecrosslinking reaction takes place, the reactive silicone preferablyincludes two or more reactive groups, preferably two or more(meth)acryloyl groups, within its molecule. In this manner, media can beobtained that exhibit high scratch resistance/abrasion resistance undervarious conditions for storage and use.

Preferably, the reactive silicone has an average molecular weight of1.0×10² or more and 1.5×10⁴ or less. The reactive silicone cannotprovide the desired lubricity when the average molecular weight is lessthan 1.0×10². On the other hand, when the average molecular weight isgreater than 1.5×10⁴, the compatibility of the reactive silicone in thecomposition for the hard coat layer tends to be decreased, makinguniform coating difficult.

The reactive silicone is preferably a compound that includes two or morereactive groups within its molecule and has a formula weight per onesilicone unit of 3000 or less. The reactive silicone may include, a sidefrom the silicone units, polyether or polymethylene units within itsmolecule.

Preferred reactive silicones are compounds represented by the formula(1) in which R on each end is (meth)acryloyl group and the silicone unitrepresented by —[Si(CH₃)₂O]_(n)— has a formula weight of 3000 or less.More preferred reactive silicones are those in which R on each end is(meth)acryloyl group and the silicone unit represented by—[Si(CH₃)₂O]_(n)— has a formula weight of 2000 or less.

In the present invention, the composition for the hard coat layerpreferably contains 5 wt % or more and 80 wt % or less of the inorganicfine particles (A), 0.01 wt % or more and 1 wt % or less of the reactivesilicone (B), and 19 wt % or more and 94.99 wt % or less of the activeenergy ray-curable compound (C) with respect to the total amount of thecomponents (A), (B), and (C). The film strength of the hard coat layertends to be reduced when the amount of the inorganic fine particles (A)exceeds 80 wt %, whereas the effect of the fine particles to improve theabrasion resistance of the hard coat layer is insufficient when theamount of the fine particles is less than 5 wt %. While the lubricity ofthe hard coat layer is improved, the hardness of the hard coat layertends to be reduced when the amount of the reactive silicone (B) exceeds1 wt %. On the other hand, the effect of the reactive silicone (B) toimprove the lubricity is insufficient when the amount of the reactivesilicone is less than 0.01 wt %. A more preferred ratio of thesecomponents in the composition for the hard coat layer is as follows: 10wt % or more and 60 wt % or less of the inorganic fine particles (A),0.01 wt % or more and 1 wt % or less of the reactive silicone (B), and39 wt % or more and 89.99 wt % or less of the active energy ray-curablecompound (C) with respect to the total amount of the components (A), (B)and (C).

The composition for the hard coat layer may contain knownphotopolymerization initiators. The photopolymerization initiator is notparticularly necessary when electron rays are used as the active energyrays. However, when ultraviolet rays are used, the initiator isnecessary. Examples of a radical photo initiator, among thephotopolymerization initiators, include DAROCURE 1173, IRGACURE 651,IRGACURE 184, and IRGACURE 907 (all of which are products manufacturedby Ciba Specialty Chemicals Inc.). The content by percentage of thephotopolymerization initiator is, for example, from about 0.5 to 5 wt %with respect to the total amount of the components (A), (B), and (C).

When necessary, the composition for the hard coat layer may contain anon-reactive organic diluent, a photopolymerization co-initiator, anorganic filler, a polymerization inhibitor, an antioxidant, anultraviolet ray absorber, a photo-stabilizer, an antifoamer, a levelingagent, a pigment, and a silicon compound and others.

In the present invention, the composition for the hard coat layer isapplied onto the light-transmitting layer (8) to form an uncured hardcoat layer. Subsequently, the active energy rays are irradiated to curethe uncured layer to form the hard coat layer (9). The composition canbe applied using any proper coating technique, including spin coating,dip coating, and gravure coating. In an alternate method in which alight-transmitting sheet is used to serve as the light-transmittinglayer (8), the hard coat layer (9) is first formed onto an elongate rawlight-transmitting sheet as described above, and disks are subsequentlystamped out from the raw sheet. In the same manner as described above,the disks are placed on the uncured resin layer (7) and the uncuredresin layer (7) is cured.

When the composition for the hard coat layer contains the non-reactiveorganic diluent, the composition for the hard coat layer is firstapplied to form an uncured hard coat layer, which is then dried byheating to remove the non-reactive organic solvent. Subsequently, theactive energy rays are irradiated to cure the uncured layer and tothereby form the hard coat layer (9). By first applying the organicdiluent-containing composition for the hard coat layer and then removingthe organic solvent by heating, the reactive silicone tends toconcentrate in the proximity of the surface of the uncured hard coatlayer. The result is more silicone existing in the proximity of thesurface of the cured hard coat layer (9). This further enhances thelubricity. The heating/drying process is preferably carried out at atemperature of for example 40° C. or more and 100° C. or less and over atime period of for example 30 seconds or more and 8 minutes or less,preferably 1 minute or more and 5 minutes or less, and more preferably 3minutes or more and 5 minutes or less. Examples of the non-reactiveorganic diluent include, but are not limited to, propyleneglycolmonomethylether acetate, propyleneglycol monomethylether, ethyleneglycolmonomethylether, butyl acetate, methyl ethyl ketone, methyl isobutylketone, and isopropyl alcohol. The active energy rays may be properlyselected from ultraviolet rays, electron rays, visible rays, and otherproper active energy rays. Preferably, ultraviolet rays or electron raysare used. The thickness of the hard coat (9) after curing is adjusted toabout 0.5 to 5 μm.

EXAMPLES

The present invention will now be described in detail with reference toexamples, which are not intended to limit the scope of the invention inany way.

[Preparation of Compositions for Hard Coat Layer]

The following base compositions (a), (b), and (c) for ultravioletray-curable materials were prepared:

(Base composition (a)) Reactive group-modified colloidal 100 parts byweight silica (dispersion medium = propyleneglycol monomethyletheracetate, non-volatile component = 40 wt %) Dipentaerythritolhexaacrylate  48 parts by weight Tetrahydrofurfuryl acrylate  12 partsby weight Propyleneglycol monomethylether acetate  40 parts by weight(Non-reactive diluent) IRGACURE 184 (Polymerization initiator)  5 partsby weight (Base composition (b)) Phenoxyethylacrylate  35 parts byweight 1,6-hexanedioldiacrylate  45 parts by weight Trimethylolpropanetriacrylate  20 parts by weight IRGACURE 184 (Polymerization initiator) 5 parts by weight (Base composition (c)) Dicyclopentanyl acrylate  30parts by weight 1,6-hexanedioldiacrylate  20 parts by weightPentaerythritol triacrylate  25 parts by weight Pentaerythritoltetraacrylate  25 parts by weight IRGACURE 184 (Polymerizationinitiator)

The reactive silicones shown in Table 1 were then added to the basecompositions (a), (b), and (c) to obtain compositions a-1, a-2, a-3,b-1, and c-1 for forming respective hard coat layers. 0.25 parts byweight of each of the reactive silicones were added to 100 parts byweight of the corresponding base composition. For the base composition(a), 0.25 parts by weight of each of the corresponding reactivesilicones were added with respect to 100 parts by weight of thenon-volatile component in the composition (a).

TABLE 1 Composition for hard coat Base layer No. composition Reactivesilicone a-1 Composition (a) X-24-8201 (Monofunctional siliconemethacrylate, molecular weight: about 2000, manufactured by Shin-EtsuChemical Co., Ltd.) a-2 Composition (a) X-22-164A (bifunctional siliconemethacrylate, molecular weight: about 1900, manufactured by Shin-EtsuChemical Co., Ltd.) a-3 Composition (a) — b-1 Composition (b) X-22-164A(bifunctional silicone methacrylate, molecular weight: about 1900,manufactured by Shin-Etsu Chemical Co., Ltd.) c-1 Composition (c)X-22-164A (bifunctional silicone methacrylate, molecular weight: about1900, manufactured by Shin-Etsu Chemical Co., Ltd.)

Examples 1 and 2, and Comparative Examples 1 to 3

A sample optical recording disk having a layered structure as shown inFIG. 1 was prepared in the following manner.

A 100 nm thick reflective layer (3) of Al₉₈Pd₁Cu₁ (in atomic ratio) wasdeposited on the surface of a grooved disk-shaped supporting substrate(2) (formed of polycarbonate, 120 mm in diameter and 1.2 mm inthickness) by sputtering. The depth of the above grooves, which isrepresented by light-path length at wavelength λ=405 nm, was set intoλ/6. The recording track pitch in the groove-recording scheme was setinto 0.32 μm.

A 20 nm thick second dielectric layer (4) was then deposited on thesurface of the reflective layer (3) by sputtering using an Al₂O₃ target.On the surface of the second dielectric layer (4), a 12 nm thickrecording layer (5) was then deposited by sputtering using an alloytarget formed of a phase-changing material. The composition of therecording layer (5) (in atomic ratio) was Sb₇₄Te₁₈ (Ge₇In₁).Subsequently, a 130 nm thick first dielectric layer (6) was deposited onthe surface of the recording layer (5) by sputtering using a ZnS (80 mol%)-SiO₂ (20 mol %) target.

A solution of an ultraviolet ray-curable resin that can undergo radicalpolymerization (4X108E, manufactured by MITSUBISHI RAYON, solvent=butylacetate) was then applied onto the surface of the first dielectric layer(6) by spin-coating to form a resin layer (7). The solution was appliedin such a manner that the resulting resin layer (7) was 2.0 μm thickafter curing.

Subsequently, a 100 μm thick polycarbonate sheet was placed on the resinlayer (7) in vacuum (0.1 atm or below). PUREACE (manufactured by Teijin)produced by flow-casting was used as the polycarbonate sheet. Thepressure was then allowed to return to atmospheric pressure andultraviolet rays were irradiated to cure the resin layer (7). As aresult, the polycarbonate sheet was adhered to the resin layer (7) toserve as a light-transmitting layer (8).

One of the compositions for respective hard coat layers, i.e., a-1(Example 1), a-2 (Example 2), a-3 (Comparative Example 1), b-1(Comparative Example 2), and c-1 (Comparative Example 3), was thenapplied onto the surface of the light-transmitting layer (8) byspin-coating. Ultraviolet rays were then irradiated to cure thecomposition and to thereby form a hard coat layer (9). The sameprocedures were followed to prepare a sample disk for each composition.For each composition, the hard coat layer (9) was approximately 1.5 μmthick after curing. For the compositions a-1, a-2, and a-3, the disk washeated at 60° C. for 3 minutes after application of the composition andprior to exposure to ultraviolet rays to remove the diluent solventremaining in the coating and to thereby form the hard coat layer (9).

In this manner, sample optical recording disks No. 1 (Example 1), No. 2(Example 2), No. 3 (Comparative Example 1),

No. 4 (Comparative Example 2), and No. 5 (Comparative Example 3) wereprepared.

Comparative Example 4

A sample optical recording disk No. 0 was prepared in the same manner asin Example 1, except that the hard coat layer (9) was not formed.

(Evaluation)

The following performance tests were conducted on each of the sampleoptical recording disks No. 0 through No. 5 prepared in Examples 1 and 2and Comparative Examples 1 through 4.

(1) Degree of Warp in the Disk Surface (Tilt)

Using a machine accuracy-measuring apparatus DC-1010C (manufactured byCORES), each sample disk was measured for the tilt angle (deg.) alongthe radius of the disk. The sample disks were measured for the initialtilt angle and the tilt angle after the disks were stored in a hightemperature, high humidity environment (Temperature=80° C., Relativehumidity 85%, Storage period=100 hours). The results are shown in Table2 below. In Table 2, positive numbers indicate that the disks werewarped concavely toward the light-transmitting layer and negativenumbers indicate that the disks were warped in the opposite direction.

(2) Scratch Resistance During Contact with an Optical Head

Using an optical disk evaluation apparatus (DDU1000, manufactured byPULSTEC), the optical head contact test was conducted in the followingmanner: Each sample optical disk was mounted on a spindle motor of theevaluation apparatus with the hard coat surface facing upward. Theheight of the optical head was adjusted so that the distance between thetip of the optical head and the surface of the optical disk wasapproximately 0.5 mm. The spindle motor was operated at 2000 rpm and thefocus servo of the apparatus was activated to drive the actuator of theoptical head. This caused the tip of the optical head to repeatedly comeinto contact with the hard coat surface of the optical disk at certaintime intervals. After 10 contacts between the tip of the optical headand the hard coat surface of the optical disk, the focus servo wasdeactivated and the optical disk was removed. The hard coat surface ofthe optical disk was visually inspected for the presence or absence ofscratches. Five sample optical disks were tested for each of Examplesand Comparative Examples, and the scratch resistance was evaluated basedon the number of the scratched samples. For the sample optical disks ofComparative Example 4, visual inspection for the presence or absence ofscratches was performed on the surface of the light-transmitting layer.

The optical head mounted on the evaluation apparatus included a plasticobjective lens surrounded by a disk-shaped ABS-resin protective plate.It was this protective plate that came into contact with the hard coatsurface during the test.

(3) Coefficient of Friction

According to the scheme depicted in FIG. 2, the coefficient of frictionof the hard coat surface was determined for each sample optical disk.The sample disks were measured for each of the initial coefficient offriction, the coefficient of friction after the disks were stored in ahigh temperature, high humidity environment (Temperature=80° C.,Relative humidity=85%, Storage period=100 hours), and the coefficient offriction after the disks were stored in a high temperature, low humidityenvironment (Temperature=80° C., Relative humidity=lower than 5%,Storage period=100 hours).

As shown in FIG. 2, a sample optical disk (1) was mounted on a spindlemotor (21) with the hard coat surface (9) facing upward. A 10 mm wide,100 mm long strip (22) of non-woven fabric (Bemcot Lint-Free CT-8,manufactured by Asahi Kasei Co., Ltd.) was placed on the hard coatsurface (9) of the optical disk, and a weight (24) was placed on one end(22 a) of the non-woven fabric (22) to apply a load of 0.1 N/cm². Theweight (24) was positioned about 40 mm radially away from the center ofthe disk and the non-woven fabric (22) was oriented so that the lengthdirection thereof was perpendicular to the radial direction connectingthe center of the disk to the position of the weight (24). With theother end (22 b) of the non-woven fabric (22) anchored to a transducer(23), the optical disk (1) was rotated at a rate of 600 rpm and thefrictional force acting upon the non-woven fabric (22) was detected bythe transducer (23) to determine the coefficient of friction.

The sample optical disk No. 0 of Comparative Example 4 proved to have asignificantly low scratch resistance of the surface of thelight-transmitting layer: the samples received significant scratchesduring the measurement under the above-described conditions. The resultsof the measurement of the coefficient of friction of the sample opticaldisks No. 1 to No. 3 are shown in FIG. 3 (cumulative number of rotationversus coefficient of friction).

TABLE 2 Tilt (Radial direction, unit: deg) Sample Composition After thestorage Scratch resistance optical disk for hard coat in a hightemperature, (Number of No. layer No. Initial high humidity environmentthe scratched samples) Comparative No. 0 — 0.09 0.03 5 Example 4 Example1 No. 1 a-1 0.15 0.23 0 Example 2 No. 2 a-2 0.10 0.24 0 Comparative No.3 a-3 0.08 0.15 5 Example 1 Comparative No. 4 b-1 0.15 0.21 3 Example 2Comparative No. 5 c-1 0.32 0.51 0 Example 3

The results are shown in Table 2.

As can be seen from Table 2, the initial warp was significantly smallfor each of the sample optical disks No. 1 and No. 2 and remained smallafter storage in high-temperature, high humidity environment. Thus, thesample optical disks No. 1 and No. 2 proved to be suitable for practicaluse. None of the five samples of No. 1 and No. 2 received scratches inthe optical head contact test. The samples also showed significantlyhigh initial scratch resistance.

As shown by the results of the measurement of the coefficient offriction in FIG. 3, the coefficient of friction of the sample No. 1 wasinitially small, indicating that the scratch resistance, or lubricity,of the sample No. 1 was initially as high as that of the sample No. 2.The sample No. 1, however, showed somewhat higher coefficient offriction as compared to the sample No. 2. The difference becamesignificant especially after storage in high-temperature, low humidityenvironment. The reason for this is considered to be as follows: sincethe silicone acrylate used in the sample No. 1 was monofunctional, thecrosslinking between the silicone acrylate and the base material couldnot proceed to a sufficient degree. This could result in the degradationor evaporation of the unreacted silicone acrylate, or migration of theunreacted silicone acrylate into the depth of the coating film underhigh temperature conditions. As a result, the silicone density on thehard coat surface was decreased, leading to a high coefficient offriction. In comparison, the crosslinking between the highly reactivebifunctional silicone acrylate and the base material proceeded to a highdegree in the sample No. 2, so that the silicone density on the hardcoat surface of the sample No. 2 was not significantly decreased evenunder high temperature conditions. As a result, only slight increase wasobserved in the coefficient of friction even after storage in hightemperature, low humidity environment. Thus, it can be inferred that thesample No. 2 can retain high scratch resistance after storage in a hightemperature environment, in particular, in a high temperature, lowhumidity environment. These observations suggest that bifunctional orhigher polyfunctional silicones are suitable for use as the reactivesilicone.

All of the five of the sample optical disks No. 3 received scratches inthe optical head contact test. Although the hard coat layers of thesamples No. 3 used the same base material (a) as that used in thesamples No. 1 and No. 2 and thus had a high hardness, the lack of thereactive silicone in the hard coat agent resulted in insufficientlubricity of the hard coat surface, making the samples susceptible toscratches.

The sample optical disks No. 4, which used the base material (b) withinsufficient hardness, received scratches in three samples in theoptical head contact test despite the addition of the reactive siliconeto impart lubricity to the hard coat surface.

The sample optical disks No. 5, which used the silica fine particle-freebase material (c), were resistant to scratches in the optical headcontact test. Nevertheless, the large initial tilt angle and the largetilt angle observed after storage in a high temperature, high humidityenvironment suggest that these disks are not suitable for use as opticaldisks. While increasing the ratio of the polyfunctional monomer or thepolyfunctional oligomer in the base material increased the hardness ofthe base material, the contraction of the material upon curing was alsoincreased significantly, leading to unfavorably large tilt angles.

In the above-mentioned Example, the hard coat layer was given to thephase-change type optical disks. However, the present invention can beapplied to read-only type optical disks or write-once type optical disksas well as optical disks having a phase-change type recording layer.Therefore, the above-mentioned working examples are merely examples inall points, and the present invention should not be restrictedlyinterpreted by the examples. Furthermore, all modifications belonging toa scope equivalent to that of the claims are within the scope of thepresent invention.

INDUSTRIAL APPLICABILITY

According to the present invention, an optical information medium thatis less susceptible to warp in the disk surface while offeringsignificantly high scratch resistance and abrasion resistance isprovided. According to the present invention, a method for producing anoptical information medium that is less susceptible to warp in the disksurface while offering significantly high scratch resistance andabrasion resistance is provided.

1. An optical information medium comprising a supporting substrate and afilm element, the film element disposed on the supporting substrate andcomposed of one or more layers including at least a recording layer or areflective layer, wherein at least one of the supporting substrate-sidesurface and the film element-side surface is formed of a hard coat layerof a cured product of a composition comprising: (A) inorganic fineparticles with an average particle size of 100 nm or less; (B) areactive silicone; and (C) an active energy ray-curable compound.
 2. Theoptical information medium according to claim 1, wherein the inorganicfine particles (A) are fine particles of a metal or a semi-metal oxide,or fine particles of a metal or a semi-metal sulfide.
 3. The opticalinformation medium according to claim 1, wherein the inorganic fineparticles (A) are fine particles of silica.
 4. The optical informationmedium according to claim 3, wherein the fine particles of silica aremodified on the surface with a hydrolyzable silane compound including anactive energy ray-reactive group.
 5. The optical information mediumaccording to claim 1, wherein the reactive silicone (B) comprises atleast one reactive group selected from the group consistingof(meth)acryloyl group, vinyl group, and mercapto group.
 6. The opticalinformation medium according to claim 1, wherein the reactive silicone(B) comprises two or more (meth)acryloyl groups within its molecule. 7.The optical information medium according to claim 1, wherein thecomposition comprises 5 wt % or more and 80 wt % or less of theinorganic fine particles (A), 0.0 wt % or more and 1 wt % or less of thereactive silicone (B), and 19 wt % or more and 94.99 wt % or less of theactive energy ray-curable compound (C) with respect to the total amountof the components (A), (B), and (C).
 8. The optical information mediumaccording to claim 1, wherein the composition further comprises aphotopolymerization initiator.
 9. The optical information mediumaccording to claim 1, wherein information is optically recorded orreproduced by the light incident upon the supporting substrate-side orthe film element-side of the information medium.
 10. The opticalinformation medium according to claim 1, wherein either one of thesupporting substrate-side surface or the film element-side surface uponwhich the light is incident is formed of the hard coat layer.
 11. Theoptical information medium according to claim 1, wherein the supportingsubstrate has a thickness of 0.3 mm to 1.6 mm.
 12. The opticalinformation medium according to claim 1, wherein the supportingsubstrate has a thickness of 0.5 mm to 1.3 mm.
 13. The opticalinformation medium according to claim 1 comprising the reflective layerhaving a thickness of from 20 nm to 200 nm.
 14. The optical informationmedium according to claim 1 comprising the recording layer comprising amaterial selected from the group consisting of Ge—Sb—Te, In—Sb—Te,Sn—Se—Te, Ge—Te—Sn, In—Se—Tl, and In—Sb—Te.
 15. The optical informationmedium according to claim 14, wherein the material comprises at leastone metal selected from the group consisting of Co, Pt, Pd, Au, Ag, Ir,Nb, Ta, V, W, Ti, Cr, Zr, Bi, and In.
 16. The optical information mediumaccording to claim 1, wherein the composition comprises 10 wt % or moreand 60 wt % or less of the inorganic fine particles (A), 0.01 wt % ormore and 1 wt % or less of the reactive silicone (B), and 39 wt % ormore and 89.99 wt % or less of the active energy ray-curable compound(C) with respect to the total amount of the components (A), (B) and (C).17. A method for producing an optical information medium, comprising thesteps of: forming, on a supporting substrate, a film element composed ofone or more layers including at least a recording layer or a reflectivelayer; applying a composition onto at least one of the surface of thefilm element and the surface of the supporting substrate opposite to thefilm element-formed side, the composition comprising (A) inorganic fineparticles with an average particle size of 100 nm or less, (B) areactive silicone, and (C) an active energy ray-curable compound; andirradiating active energy rays onto the applied composition to cure thecomposition and to thus form a hard coat layer.
 18. The method forproducing an optical information medium according to claim 17, whereinthe composition further comprises a non-reactive organic solvent, andfollowing the application of the composition and prior to theirradiation of the active energy rays to cure the composition and tothus form a hard coat layer, the non-reactive organic solvent is removedby heat-drying.
 19. The method for producing an optical informationmedium according to claim 18, wherein the heat-drying occurs at atemperature of from 40° C. or more and 100° C. or less and over a timeperiod of from 30 seconds or more and 8 minutes or less.
 20. The methodfor producing an optical information medium according to claim 18,wherein the heat-drying occurs at a temperature of from 40° C. or moreand 100° C. or less and over a time period of from 1 minute or more and5 minutes or less.